The present invention relates to the preparation of photographic emulsions, and more particularly, to a method which includes the monitoring of such preparations.
Photographic emulsions are prepared by adding to a dispersion of silver halide in gelatin various addenda such as spectral sensitizing dyes, antifoggants, grain growth modifying agents, additional silver halide and the like.
The batch-wise preparation of photographic emulsions is conventionally conducted manually by an operator who performs each step in the process by referring to a script. That is, the operator adds constituents in an amount and at a time called for by a formula. In order to make batches having the same photographic properties each batch must be prepared in the same way. The conventional procedure, however is susceptible to error. For instance, an operator may reverse the addition sequence, add constituents later in time than called for or fail to add the proper amount of a required constituent. The emulsion batch will then be different from other batches.
Without a monitoring mechanism, such errors can go undetected until after completion of the emulsion. Delaying discovery of error until this late stage wastes time and chemicals. The early discovery of an error would allow the operator immediately to abort the process. Heretofore, no suitable quantitative measure of the accuracy of the emulsion preparation process has existed.
It is known to use conductivity or resistivity measurements to determine the end point of a reaction or titration. Typical is U.S. Pat. No. 2,571,791 to Tompkins; U.S. Pat. No. 3,049,410 to Warfield et al.; U.S. Pat. No. 3,868,315 to Forster et al.; and U.S. Pat. No. 1,450,023 to Edelman. It is also known to monitor conductivity or resistivity as a function of temperature during a process to detect and control changes. This procedure is described in U.S. Pat. No. 3,278,844 to Bell et al.; U.S. Pat. No. 3,281,681 to Stevenson; and U.S. Pat. No. 3,657,640 to Jelinek et al. Conductivity has also been used for the determination of the kinetics of structure formation in binders. See U.S. Pat. No. 4,524,319 to Eberling et al. Eberling does not contemplate the addition of chemical components during the monitoring period, however. It is also known to measure conductivity of a solution and compare the conductivity reading to a conductivity taken simultaneously from a standard solution for control purposes, as shown in U.S. Pat. No. 1,951,035 to Parker. It is also known to measure changes of concentrations of fluid by measuring changes in the dielectric constant of the surrounding fluid and comparing it with pre-programmed desired levels. See U.S. Pat. No. 4,196,385 to Vestergaard et al. None of these references, however, teaches a suitable method for monitoring the preparation of a photographic emulsion so that errors in the process can be identified instantaneously.